In conventional techniques, it is not capable of adjusting pulse width of a pulse signal, which is requested in test mode of a semiconductor memory device, as much as desired. Therefore, when the pulse width is to be changed, the pulse width should be confirmed as a metal option in a delay circuit is changed step by step.
FIG. 1 provides a conventional pulse signal generating circuit for test mode and FIG. 2 shows a waveform diagram on each node in FIG. 1 step by step.
(Step I)
When power is inputted to a semiconductor memory device, a power turn-on signal pwrup is shifted from “L” state to “H” state and maintained in that state and a pulse input signal in is maintained in the “L” state. At that point, it can be seen that the logic values of a node A, a node C, a node D, a node 1 node_1 and a node 2 node_2 are maintained in the “H” state, and the logic values of a node B and an output signal out are maintained in the “L” state.
(Step II)
When the input signal in having a pulse form is shifted from the “L” state to the “H” state, the logic values of the node A and the node B go to the “L” state and the “H” state, respectively, and the output signal out goes to the “H” state.
(Step III)
The input signal in is shifted from the “H” state to the “L” state.
(Step IV)
The logic value of the node B, being in the “H” state, is transferred to the node 1 as the “L” state, after going through a second inverter 106. When the logic value of the node 1, being in the “L” state, is outputted after being delayed at a delay 107, the node 2 is shifted from the “H” state to the “L” state. At this point, when the logic value of the node D goes to the “H” state, the logic values of the node B and the output signal out are shifted to the “L” state.
As a result, it can be seen that the pulse width of the output signal out is extended by A compared to the pulse width of the input signal in. However, in such a circuit constitution, whenever the pulse width of the output signal out is to be changed, the metal option in the delay 107 should be changed step by step through FIB (Focused Ion Beam) and it costs time and expense. Further, the amount of the pulse width that can be changed should be restricted to the delay amount of that implemented delay in the circuit.